It makes no sense to try to predict what the tax laws will be in the future.
I agree but am not sure it is so clear cut. You have to ask the question - will my taxes be higher now or later, and I believe that our tax rates are at a low, and can only go up. With the deficit, rates have to go up, or government spending has to go down, or deep **** has to get deeper. My "cynic" meter pegs when talking about government spending going down, so I think taxes will go up (and the deep **** will get deeper).
So, if tax rates will be higher, then what? It is usually still good to defer taxes, but you do have to look at income levels. If you are in a higher income tax bracket now than you will be in retirement (true for most), then deferal can make a lot of sense, but because I believe taxes are currently lower than average, I would be careful and add some fudge factors in the analysis. In any case, I would prefer Roth IRA's, which do not defer taxes, but do waive taxes on earnings.
There is some intangible benefits to IRA's/401k's you also have to consider. Most people consider the money untouchable, and it is more likely that after tax funds will be spent for something than IRA/401k funds. Unless you are sure you and your spouses can clearly delimit spending and retirement savings, this may be a factor to consider.
My advice (and what I did), 3% of salary to IRA, 12% to 401k, and >10% to after tax savings. As retire@40 says, a blend, and reasons for the blend are unique to each person.
Even the wonderful Roth IRA's have their risks. The killer for those of us with Roth funds will be lower income taxes, and a consumption tax (or VAT). Nothing is a sure bet! So make your predictions on tax law - and the best bet is probably close to no/minimal change - then work thru the numbers to see what makes sense for you, but do the same thing you do with your investments - Diversify
If you want to look at tax planning,
http://i-orp.com has some tools to look at that. I would recommend it as one of the tools that should be in your arsenal of planning tools.